The present invention concerns a vibration damper for supporting vibration sensitive items, particularly electromechanical items as e.g. hard disks, floppy disk drives, CD-ROM drives and the like in relation to a base, including springs in the form of fixed bent wire pieces, each built up of a number of twisted strands, where each bent wire piece is approximately in one plane.
It is known to dampen vibrations, e.g. by rotating machines there is often inserted a damper between the machine itself and the floor surface or the base on which the machine is mounted in order to prevent that vibrations are propagated to the surroundings. There are many examples of this type of vibration dampening which dampen the vibrations satisfactorily. Dampening of vibrations arising as a result of the operation of a machine, e.g. by rotating rollers, reciprocating pistons or the like, the vibrations being in a frequency range where the dampening compared with the very large mass of the machine in itself is relatively simple, as numerous different materials and embodiments may be used. For this kind of vibration dampening is used specially reinforced rubber pads, strong springs and the like.
In the case of vibrations, including particularly transmission of vibrations from one item to another, where one item is very light at the same time as the vibrations are its a frequency range from 0–200 Hz, particularly from 0–100 Hz, there are a number of problems which have not been solved in a satisfactory way. In that the item to be isolated from vibrations is very light, traditional springs and rubber systems cannot be used, as these, due to the dead weight of the vibration sensitive item, either causes the spring to appear too stiff or result in too great an amplitude in the dampening process. Furthermore, rubber and plastic systems have the drawbacks that the spring characteristic changes as a function of the temperature, i.e. when it is very cold, the rubber becomes very hard, whereby the damper provides very little dampening at low frequencies. At the same time, rubber may decompose as a result of sunshine, oil, grease etc. whereby the service life for a rubber damper is limited. Traditional helical springs are often too rigid and have limited lifetime, as the material will suffer fatigue failure after using it a short time. A typical car spring should be chanced after about 200,000 km as there is increased probability of material failure above this limit.
From document EP 764 794 is known a vibration damper which is constructed with a base plate connected via four wire pieces to a top plate. By mounting the base plate on a base or a frame and the top plate to the element to be isolated from vibrations, according to the invention it should be possible to isolate the transmission of vibrations from the construction to the vibration sensitive item in three planes arranged perpendicularly to each other.
A corresponding system is indicated in patent publication NL 9101012, where curved wire pieces are connected from a base plate to a top plate. The intention is that the base plate is to be mounted on a frame or a construction, and that the top plate is to be connected to the vibration sensitive item, whereby the curved wire pieces are to isolate the vibration sensitive item from vibrations created in the frame or the base.
Common to these systems is that the curved wire pieces are mounted in one plane perpendicularly to the vibrator, i.e. the base.
In the following, the dampening elements will be described with reference to an X-Y-Z co-ordinate system, where the XY, XZ and YZ planes form three mutually perpendicular planes.
If a damper as illustrated in EP 764 794 is placed in a three-dimensional co-ordinate system so that the base plate is disposed in the XZ plane and the springs are placed in a plane perpendicularly to the XZ plane, e.g. in the YZ plane, the damper will function in that movements in the Y direction are absorbed by bending of the curved wire pieces, movements in the Z plane will be absorbed as rolling, and actions in the X direction will be absorbed by torsion in the curved wire pieces. An arbitrary vibration pattern will therefore be a combination of the above mentioned pattern of movement, whereby the curved wire pieces will interact with their respective spring constants for performing the desired dampening. Physically it is so that the spring constant, which is determining how a spring will react to an action, is different depending on whether the curved wire pieces are actuated by compression, rolling or torsion. Thee damper according to EP 764 794 and other comparable systems will therefore dampen differently, depending on the direction of the resultant of the vibrations that the damper is installed to isolate from. Where the item desired to be isolated from vibration influence is fixed, i.e. not movable, it may be possible to compensate for this difference in degree of dampening, as the resultant of the action has constant direction by different provisions.
The systems known from EP 764 794 and NL 9101012 may generally be denoted vibration dampers with single springs. Laboratory tests show that the so-called single spring systems only have effect at relatively high frequencies, namely around 180 Hz. Up to about 180 Hz, these systems amplifies the vibrations transmitted from the base to the vibration sensitive item. For frequencies above 180 Hz, the damper is activated and starts to reduce the influence of vibrations transmitted to the vibration sensitive item.
Electronic equipment finds still wider application and becomes a more and more integrated part of daily life. To a still greater extent, different kinds of electronics are fitted in vehicles, such as boats, ships, trains, buses, lorries, normal cars, etc., and the electronic items are therefore exposed to jolts and other non-uniform actions. Particularly with regard to jolts, electronic items or apparatuses in which there are also mechanical components are particularly exposed. This is particularly the case with CD players, CD-ROM players, hard disks and similar apparatuses, which besides very sensitive electronics also consist of very sensitive mechanics. In order that these installations may also operate optimally, it is desirable to dampen the vibration transmission from the vehicle/ship/train/bus/car itself and to the electro-mechanical component.
Particularly concerning installation of electronic equipment, as e.g. hard disks, CD-ROM drives, or other sensitive equipment in ships, trains, buses, vehicles, airplanes and other locations, where vibrations below 180 Hz are generated, i.e. at relatively low frequencies, the prior art single spring systems are thus unsuitable as they have a negative effect on the total vibration transmission to vibration sensitive items.
There is therefore a need for providing a vibration damper suited for isolating light vibration sensitive elements from a vibration generating base at relatively low frequencies.